Prevalence and associated factors of overweight in Chinese adolescents: A cross‐sectional study

Abstract Background and Aim Obesity has been a global public health issue due to the increasing mortality rate and prevalence among children. However, there are scarce studies on obesity prevalence in Hong Kong children. The study aims to identify the risk factors of obesity among primary and secondary school students by assessing the relationship between sociodemographic factors, health‐related behaviors, and social relationships. Methods Self‐administrated surveys were collected from 30 primary schools and 25 secondary schools participating in the “Quality Education Fund Thematic Network on Health Schools” project. Descriptive analysis was conducted to examine the proportions of different characteristics and to compare the disparity between primary and secondary school students with obesity. Results A total of 4884 responses were collected. A larger proportion of primary school students with obesity were male (adjusted odds ratio [aOR]: 2.55, 95% confidence interval [CI]: 1.77–3.67, p < 0.001) and actively gamed (aOR: 1.64, 95% CI: 1.07–2.51, p = 0.024). Secondary school students with obesity were male (aOR: 1.61, 95% CI: 1.21–2.13, p = 0.001), had poor self‐perceived academic performance (aOR:1.51, 95% CI: 1.10–2.08, p = 0.011) and expressed higher life satisfaction (family) (aOR: 1.13, 95% CI: 1.01–1.26, p = 0.032). There were negative associations found between obesity and physical activity, high consumption of sugary drinks, chocolate or candies, and insufficient consumption of vegetables. Conclusion Male sex, physical inactivity, low self‐perecived academic performance, and poor dietary behaviors were the risk factors for obesity among primary and secondary school students. The findings highlighted the importance of identifying younger individuals who were at risk of becoming clinically obese. Further studies should explore the effectiveness of various interventions through longitudinal study.


| INTRODUCTION
Obesity is a global health issue in the 21st century.2][3] A total of 39 million children below the age of five reported having health issues caused by obesity. 1 According to the World Health Organization (WHO), obesity has killed more people than malnourishment in countries where the majority of the world's population is living. 1,2owth standards and health assessment have been developed by the Department of Health to detect obesity in the youth population, specifically targeting primary and secondary school students in Hong Kong. 4,5Obesity is defined as having a body weight of more than 120% of the median value of weight for height.This is used to assess male students who are between 55 cm and 175 cm tall and female students who are 55 cm and 165 cm tall, with a body mass index (BMI) larger than 25. 4 Rates of obesity have increased from 16.4% to 21.4% and 12.6% to 18.7% among primary school students and secondary school students respectively from the 1997/1998 school year to the 2010/2011 school year. 5,6mpared to children of a healthy weight, overweight children reported more negative experiences and significant practical and psycho-social problems.For example, poor health status and diseases, low self-esteem, poor school performance, and a higher risk of being bullied. 6,7This could also result in poor health status and reduced employment and marital prospects in adulthood. 8,9]5,6 Healthy behaviors may include 60 min of moderate to highintensity physical activities every day, controlling sugar and fat intake, and sufficient intake of vegetables and fruits. 5,6Education about maintaining a healthy weight has been suggested to target families with children who are at risk of obesity as indicated by high BMI values or high birth weight. 61][12] Early preventive strategies have been evaluated in a study involving 64 German kindergartens.Positive behavioral changes were observed as vegetable and fruit consumption increased among children. 12,13wever, studies regarding the prevalence of obesity in children are still limited in Hong Kong. 14,15This study aims to identify the risk factors of obesity among primary and secondary school students by assessing the relationship between sociodemographic factors, healthrelated behaviors, and their social relationships.This helps identifiying individuals who are at risk of obese at an early stage and develops preventive measures targeting high-risk adolescents.

| Participant recruitment
This study recruited students from local primary and secondary schools participating in the project "Quality Education Fund Thematic Network on Health Schools."The project was carried out by the Centre for Health Education and Health Promotion of the Chinese University of Hong Kong (CHEHP).A total of 30 primary schools and 25 secondary schools participated in this project.

| Data collection
There were several procedures for survey collection.First, students were informed that participation was voluntary and data collection would be anonymized to protect privacy of the students.Students were assured that their responses would be confidential and their grades would remain unaffected by their participation or responses.
Second, parental consent and consent from the school were collected before conducting the survey.Third, training was provided to the interviewers who were responsible for informing students about the purpose and features of the survey.Fourth, the confidentiality of the data collected was emphasized.Class teachers helped to identify students who had parental consent to participate in the study.However, they were not involved in answering student queries and did not have access to the questionnaire responses.

| Survey instruments
The survey was validated using pilot tests and approved by expert panels consisting of epidemiologists, healthcare professionals, and physicians.There were 19 questions in the survey, consisting of Traditional Chinese and English version.Sociodemographic information including sex, age, number of household computers, ownership of cars (household), ownership of private bedroom, traveling history in the past 12 months, self-perceived academic performance, and self-reported expectations from parents (Questions 1-5) were collected from participants.Health-related parameters including the presence of mental health outcomes such as psychological distress, depression, and self-harm, weight and height, weight control, and frequency of physical activity of at least moderate intensity were examined.Only secondary school students reported the quality of their sleep (Questions 6-13).Social relationships were assessed using the number of friends, the experience of being bullied at school and online, and the life satisfaction level of family and friends (Questions 14-17).Lastly, participants were required to report experiences of drinking alcohol and smoking (Questions 18-19).A 5-point Likert scale has been used in the survey.The detailed questionnaire has been provided in Supporting Information S1: Material 1.

| Variables
In this study, obesity was defined according to the assessment guide of childhood growth and nutrition published in 1995 (reference).
Students were classified into "overweight," "normal range," and "underweight" according to their sex, height, and weight.Overweight refers to those whose weight exceeds 120% of the median of the weight and height status; normal range refers to those who weigh between 80% and 120% of the median, and underweight refers to those whose weight is below 80% of the median. 16If the height of boys or girls exceeds 175 cm or 165 cm respectively, BMI cutoff points for the Asian population were used for classification.For example, the range of 18.5-22.9kg/m 2 would be classified as normal weight. 17e Family Affluence Scale (FAS) was used to measure socioeconomic status.Psychological distress of mental health outcomes was measured by using the Kessler Psychological Distress Scale (K6) with a cutoff score of 13. 18,19 Depression was defined as a prolonged feeling of despair whereas having any intention, plans, attempts or experience in injuring themselves or committing suicide was counted as self-harm.The Pittsburgh Sleeping Quality Index (PSQI) was used to evaluate sleep quality.Detailed coding of the variables has been listed in Supporting Information S1: Material 2.

| Respondents' characteristics
A total of 4884 responses were collected with 2234 (45.7%) reponses from primary school students and 2650 (54.3%) responses from secondary school students.The overall prevalence of obesity was 17.3% and 16.8% for primary and secondary school students respectively.The sex proportions of the two groups were largely balanced, with 49.5% (n = 1310) primary school cohort and 51.6% (n = 1146) of the secondary school cohort being male.Significant variations in socioeconomic status, self-perceived academic performance, and parental expectation were observed across the two groups.

| Prevalence of overweight among patients with various characteristics
Overall, male primary school students had a significantly higher prevalence of being overweight (22.0% vs. 12.4%, p < 0.001).Furthermore, a higher prevalence of overweight was found among primary school students who had poor self-perceived academic performance (24.6% vs. 14.2%-16.3%[good to average], p < 0.001), spent more than 2 h on gaming (24.6% vs. 15.7%,p < 0.001) and social media (23.9% vs.
Full results (aORs and their 95% CIs) of the regressions are included in Table 3.

| Summary of major findings
The results of this study found that male sex, poor self-perceived academic performance, and higher sugar and fat intake were the main characteristics of both primary and secondary students who had a higher prevalence of obesity.Compared with primary school students, secondary school students were more active in gaming and social media and inactive in physical activity.They were more likely to have an unhealthy diet, such as having more sugar and fat intake and fewer vegetables or fruits, and to experience psychological distress.It has been found that primary school students who were active in gaming and had a behavior of skipping breakfast were more likely to be overweight.Among secondary school students, physical inactivity, satisfaction with family, and consumption of processed or preserved meat were the causes of obesity, while those who had an unhealthy diet of high-consuming sugar drinks, chocolate, or candies and insufficient consumption of vegetables were less likely to be overweight.

| Risk factors associated with overweight or obesity among students
The sex difference between overweight and obesity among students has been proven.Studies have found that the increase in obesity rates in boys was greater than that in girls, by 151% and 81%, respectively. 10,20Across 188 countries, there were 65% of the countries reported that a higher prevalence of obesity has been found in boys aged 5-9 years than those in girls, and 60% of countries reported a similar trend among those aged 10-19 years. 212][23][24][25] The differences might be due to biological differences in body composition between sexes and sociocultural influences.For example, leptin level which helped suppress appetite and promote energy utilization was higher among females than males. 21,26Besides, gender-based stereotypes also required females to eat less, and be healthier and thin.Therefore, girls would have more weight-related concerns than boys, especially in high-income countries. 21,27,28It was common that male students were more likely to have obesity issues.
The poor academic result was also a key characteristic of secondary school students who are overweight.A study based on a national youth risk behavior survey has found that youth aged 14-17 years and classified as overweight were less likely to report higher grades (OR 0.79, 95% CI: 0.68-0.91,p = 0.002).The result has shown that being overweight was significantly related to academic performance. 28Another study also found a significant association between overweight status and poorer school performance.Children who were teased about their weight barely had strong school performance. 29A study that examined the relationship between nutritional status and academic performance of primary school students aged 9-10 years old in Malaysia has found that academic performance was correlated with BMI, income and educational level of their parents, and whether they have taken breakfast. 30However, another study in Kuwait did not find any association between obesity and academic performance in the classroom setting among 1066 male students. 31e relationship between overweight and obesity and academic performance was still critical.
The current study suggested that primary school students, in general, had better socioeconomic status, self-perceived academic performance, and higher self-reported expectations from parents which are similar to a previous study where the prevalence of overweight and obesity was examined in 6729 children and significant differences were reported between the highest and the lowest SES group. 32Children who were from the lowest SES group which was measured by the index of community socioeducational advantage (ICSEA) based on parents' occupation and education, school geographical location and the proportion of indigenous students had a lower level of educational advantage, and had a higher prevalence of overweight and obesity among schools.It has been suggested that children from lower SES backgrounds had lower levels of physical activity, higher consumption of fast food and sugar-sweetened soft drink, and were more difficult to receive and actively respond to health promotion messages.][34] among secondary school students might have been overestimated due to the lower proportion of participants from Hong Kong Island.
This was because significant association was found between overweight and socioeconomic status, yet, residents in Hong Kong Island had a better socioeconomic status.Furthermore, generalizing the findings of this study to other populations should be done meticulously due to the nonrandom sampling adopted to collect the data and the uneven responses of each school.Additionally, due to the cross-sectional design of the study, the causal relationship was not evaluated as the time series of the occurrence of the two events cannot be identified.Nevertheless, the association identified in this study provided the foundation for future longitudinal studies to explore the risk factors as causal factors.

| CONCLUSION
The current study identified individuals with a higher risk of being overweight by multivariable logistic regression.Factors associated with being overweight included the male sex, physical inactivity, poor self-perceived academic performance, and unhealthy dietary habits.
Hence, multifactorial intervention such as immediate and intensive lifestyle modification is crucial.Future studies should explore the effectiveness of various interventions after examining the associations with a longitudinal study.

IBM
Statistical Package for Social Sciences (SPSS) software version 26.0 was used to conduct statistical analyses.The descriptive analysis examined the characteristics of the study participants including the disparity between the primary and secondary school students.The difference in respondents' characteristics was presented in proportions with the outcome variables.Separate binary regression models were designed to examine the association between the risk factors and outcome variables (overweight).Also, multiple logistic regression models were used to examine the explanatory association between factors and the outcome variables after adjustment.All p-values less than 0.05 were considered statistically significant.
Prevalence of overweight among students with various characteristics.